Preprints
https://doi.org/10.5194/acp-2022-695
https://doi.org/10.5194/acp-2022-695
 
13 Oct 2022
13 Oct 2022
Status: this preprint is currently under review for the journal ACP.

Linking gas, particulate, and toxic endpoints to air emissions in the Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM) version 1.0

Havala O. T. Pye1, Bryan K. Place2, Benjamin N. Murphy1, Karl M. Seltzer2,3, Emma L. D'Ambro1, Christine Allen4, Ivan R. Piletic1, Sara Farrell2, Rebecca H. Schwantes5, Matthew M. Coggon5, Emily Saunders7, Lu Xu5,6, Golam Sarwar1, William T. Hutzell1, Kristen M. Foley1, George Pouliot1, Jesse Bash1, and William R. Stockwell8 Havala O. T. Pye et al.
  • 1Office of Research and Development, US Environmental Protection Agency, Research Triangle Park, North Carolina, USA
  • 2Oak Ridge Institute for Science and Engineering (ORISE) Postdoctoral Program at the Office of Research and Development, US Environmental Protection Agency, Research Triangle Park, North Carolina, USA
  • 3Office of Air and Radiation, US Environmental Protection Agency, Research Triangle Park, North Carolina, USA
  • 4General Dynamics Information Technology, Research Triangle Park, North Carolina, USA
  • 5NOAA Chemical Science Laboratory (CSL), Boulder, Colorado, USA
  • 6Cooperative Institute for Research in Environmental Science (CIRES), University of Colorado, Boulder, Colorado, USA
  • 7Office of Chemical Safety and Pollution Prevention, US Environmental Protection Agency, Washington D.C, USA
  • 8University of Texas at El Paso, El Paso, Texas, USA

Abstract. Chemical mechanisms describe the atmospheric transformations of organic and inorganic species and connect air emissions to secondary species such as ozone, fine particles, and hazardous air pollutants (HAPs) like formaldehyde. Recent advances in our understanding of several chemical systems and shifts in the drivers of atmospheric chemistry warrant updates to mechanisms used in chemical transport models such as the Community Multiscale Air Quality (CMAQ) modeling system. This work builds on the Regional Atmospheric Chemistry Mechanism version 2 (RACM2) and develops the Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM) version 1.0, which fully couples the chemistry leading to ozone and secondary organic aerosol (SOA) with consideration of HAPs. CRACMM v1.0 includes 178 gas-phase species, 51 particulate species, and 508 reactions spanning gas-phase and heterogeneous pathways. To support estimation of health risks associated with HAPs, nine species in CRACMM cover 50 % of the total cancer and 60 % of the total noncancer health risk estimated for primary HAPs from anthropogenic and biomass burning sources in the U.S., with the coverage of risk higher (>80 %) when secondary formaldehyde and acrolein are considered. In addition, new mechanism species were added based on the importance of their emissions for ozone, organic aerosol, or atmospheric burden of total reactive organic carbon (ROC): sesquiterpenes, furans, propylene glycol, alkane-like low to intermediate volatility organic compounds (9 species), low to intermediate volatility oxygenated species (16 species), intermediate volatility aromatic hydrocarbons (2 species), and slowly reacting organic carbon. Intermediate and lower volatility organic compounds were estimated to increase the coverage of anthropogenic and biomass burning ROC emissions by 40 % compared to current operational mechanisms. Autoxidation, a gas-phase reaction particularly effective in producing SOA, was added for C10 and larger alkanes, aromatic hydrocarbons, sesquiterpenes, and monoterpene systems including second generation aldehydes. Integrating the radical and SOA chemistry put additional constraints on both systems and enabled the implementation of previously unconsidered SOA pathways from phenolic and furanone compounds, which were predicted to account for ~30 % of total aromatic hydrocarbon SOA under typical atmospheric conditions. CRACMM organic aerosol species were found to span the atmospherically relevant range of carbon number, number of oxygens per carbon, and oxidation state with a slight high bias in number of hydrogens per carbon. In total, eleven new emitted species were implemented as precursors to SOA compared to current CMAQv5.3.3 representations resulting in a bottom-up prediction of SOA, which is required for accurate source attribution and design of control strategies. CRACMMv1.0 will be available in CMAQv5.4.

Havala O. T. Pye et al.

Status: open (until 04 Dec 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Havala O. T. Pye et al.

Data sets

Data for the Community Regional Atmospheric Chemistry Multiphase Mechanism (CRACMM) version 1.0 Havala O. T. Pye https://doi.org/10.23719/1527956

Model code and software

CMAQ Repository US Environmental Protection Agency https://github.com/USEPA/CMAQ

CRACMM Repository Havala O. T. Pye and US Environmental Protection Agency https://github.com/USEPA/CRACMM

Havala O. T. Pye et al.

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Short summary
Chemical mechanisms describe how emissions from vehicles, chemical products, vegetation, and other sources are chemically transformed in the atmosphere to secondary products. The Community Regional Atmospheric Chemistry Multiphase Mechanism is a new mechanism that integrates radical chemistry leading to gas-phase endpoints with pathways to fine particle mass. In addition, some hazardous air pollutants are explicitly included to enable calculation of health risks from specific chemicals.
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